I think it's actually how quickly the sight's recenter after firing, not quite recoil.

Recoil is the weapon bounce as you fire - how far it travels with each shot - especially in automatic fire mode.

Handling is "the spread" effect you can see from the crosshairs -- they widen as you move and narrow when you stand still. The time it takes to narrow and such.

That widening is the area that your bullets may land in so if you move and fire -- as in strafe or backing away from mutants as you shoot.. handling is important so you will hit more. For standing still shooting? it's not that important.

Handling means how quickly you can move your point of view in-game - for example, the PKM from Clear Sky and Call of Pripyat has a notoriously low handling, resulting in very slow turning when compared to most other guns in-game. It also affects how fast the reticle will return to the normal mode after moving, or doing some other actions that result in your reticle getting bigger ( = less accurate)